3 Phase power keeps on tripping

[Daveh36]

Hi Guys any advice on this one will be a major help.
Was called out to a loss of power turned up expecting a breaker down as usual but not the case.
so here goes the problem- an apartment block with 315 amp incoming fuses feeding 400 amp mccb set to trip at 220. This in turn feeds a rising busbar with several tap off units and 250amp mccb feeding the apartment fuses and meters. No faults show when tested out but every night it trips taking out the 400amp mccb and all three main fuses.
Anyone any ideas on why this is happening. Please help as at my wits end with this one

 

[Lucien Nunes]

At this point I would be camping in the riser listening carefully around fault time.

 

[pc1966]

At this point I would be camping in the riser listening carefully around fault time.

I wonder if you could get a few long-lasting audio recorders set up in strategic locations?

Easier than camping out for a day or so!

 

[marconi]

At this point I would be camping in the riser listening carefully around fault time.

I would arm myself with a spanner or screwdriver, as required, and some electrician's gloves and goggles and then open up the riser and switchgear and simply have a look with my eyes during daytime!

 

[Daveh36]

someone hasnt got a funny kind of farm in the flats have they?

My first thought lol as come across lots of farming but wouldn't account for it

 

[marconi]

Very true the regular timing of the fault suggests something is a trigger for it.

I can't see high over-voltage (i.e. 8-10kV as mentioned in the article) being the cause as otherwise we would have lots of flat residents complaining of damaged electronics. Still, it would be a good idea to consider having some decent-sized SPD fitted to the incoming supply (e.g. a "type 1+2" and some 100A fuses/MCCB or similar for fault protection).

But the idea that DNO changes are causing electrodynamic forces in a busbar somewhere is very intriguing to me. I was pondering on how you could have a system working perfeclty for a period and then BANG! go the incomer fuses. I was wondering if the rises or one of the fuse cabinets was adjacent to a lift or something that was occasionally hitting it? But maybe there is a loose bar and DNO tap-changing is making it flap?


Yes, a very depressing event all round

I was not clear enough. I meant the electrodynamic forces act on the arc - Fleming's left hand rule. This is illustrated by some time-lapse photos in the reference in one of my earlier posts.

 

[marconi]

Daveh36: Good evening Sir. Had you thought (hoped or wished?) I'd gone away

Just wondered if you had any further developments if only to inform more on the problem? I need things to think about 'cos my wife is back in hospital.

 

[Daveh36]

Oh dear that's not good hope all is ok. On the tripping front though since I replaced the mccb again and got DNO to monitor incoming supply things seem to have settled down (famous last words). I'm thinking they had an issue with the supply but are not for telling me. Fingers crossed for now as it's not gone off in week given my hair chance to grow back haha

 

[timbobelfast]

Oh dear that's not good hope all is ok. On the tripping front though since I replaced the mccb again and got DNO to monitor incoming supply things seem to have settled down (famous last words). I'm thinking they had an issue with the supply but are not for telling me. Fingers crossed for now as it's not gone off in week given my hair chance to grow back haha

It sounds like a head scratcher indeed.

If it continues to trip, check if there is a Telecom Cabin on the rooftop somewhere. As these are normally full of AC-DC rectifiers and PSUs.

Failing that, get the LL to have an Electrical Installation Condition Report on the subs and LL services.

 

[marconi]

Daveh36: Has this problem been resolved or 'simply gone away'? Be interested to know.